Engine Tuning Issues

[sstock]

I'm still trying to wrap my head around this. I'm ok with dual quads on a tunnel, don't get me wrong but basically. if I'm seeing this right, you have two separate plenums each with their own carb feeding 4 cylinders. Each carb is running their own choke. I dunno, I don't know why but I feel safer with a manifold open to all intake runners not just 1/2, even though I understand just by the nature of the firing order and how the intake runners are configured, you will have some cylinders leaner than others. Another thing, I like to tune with a wide band 02 sensor, you could have one carb out to lunch lean and the other rich and see just a perfect air fuel ratio unless you had bungs in every pipe. I just can't get a warm and fuzzy feeling over their design. But I want to hear everyones opinion too.
This thread has been a really good read and informative.
Steve

 

[sstock]

 

[Wild Mango]

Oh, I forgot to ask a dumb question, if I get to the point of needing to add the air bleeds in the butterflies (and I suppose I will), does this get done on the primary side of each carb, or secondary side also?

Just the primaries. Start with a 1/8" hole in each, can always go a bit bigger, but carefully, 1/64" at a time.

 

[Screaming Metal]

What he said! Fronts only....

I'm still trying to wrap my head around this. I'm ok with dual quads on a tunnel, don't get me wrong but basically. if I'm seeing this right, you have two separate plenums each with their own carb feeding 4 cylinders. Each carb is running their own choke. I dunno, I don't know why but I feel safer with a manifold open to all intake runners not just 1/2, even though I understand just by the nature of the firing order and how the intake runners are configured, you will have some cylinders leaner than others. Another thing, I like to tune with a wide band 02 sensor, you could have one carb out to lunch lean and the other rich and see just a perfect air fuel ratio unless you had bungs in every pipe. I just can't get a warm and fuzzy feeling over their design. But I want to hear everyones opinion too.
This thread has been a really good read and informative.
Steve

A tunnel with the 2 carbs on a open plenum change to balance things, the intake pulses, and slight differences in carburation, acceptable, a tunnel with 2 carbs, each its own plenum per set of 4 cylinders....only with FI and a computer. I don't believe you can get that close with carbs unless you set them up to run on the flowbench before installation.
I have know people to do it and get good results. BUT, you have to tuneeach carb, and it has to be extremely precise. Then its still marginal, thats the reason for the common plenum between the 2 carbs.

Everyone likes the 2x4 tunnels, but the 1x4 tunnel is very underrated. These were designed for hi-torque situations down low, but does not sacrifice top end power. They were designed for boat racers in mind, and others where torque was needed and wanted....like....ON THE STREET....

 

[sstock]

What he said! Fronts only....

A tunnel with the 2 carbs on a open plenum change to balance things, the intake pulses, and slight differences in carburation, acceptable, a tunnel with 2 carbs, each its own plenum per set of 4 cylinders....only with FI and a computer. I don't believe you can get that close with carbs unless you set them up to run on the flowbench before installation.
I have know people to do it and get good results. BUT, you have to tuneeach carb, and it has to be extremely precise. Then its still marginal, thats the reason for the common plenum between the 2 carbs.

Everyone likes the 2x4 tunnels, but the 1x4 tunnel is very underrated. These were designed for hi-torque situations down low, but does not sacrifice top end power. They were designed for boat racers in mind, and others where torque was needed and wanted....like....ON THE STREET....

Thanks for your informative reply, still working on my single tunnel (interesting outcome)which I'll post up on my own thread.

 

[Screaming Metal]

let me just say this, with Mr.Fix-Its setup, the guy that puts this system together is top notch....as long as all the carb adjustments are exactly where they need to be. And the plenums, the setup looks sweet.
With the reduction in the volume and the carbs, as long as they're precisely set, and flow the same, everythings cool. BUT, the screw up potential is way on up there....alot more than a 2x4 hi-rise dual plane.
That being said, if one carb screws up, well, not gonna drive far until THAT carb is fixed. On a 2x4 tunnel with a open plenum, you can run off one carb, might run like ass, but they'll usually get you home.

I am impressed with Mr. Fix Its setup....and I'm hard to impress. That guy has some incredible quality control.

 

[sstock]

Impressively put Mr. Screaming. Kudos for Colorado's quality control.